1. Field of the Invention
The present invention relates to a method of establishing an uplink in a mobile satellite communication system. More particularly, the present invention relates to a method of establishing an uplink that enables a terminal to calculate a delay time to thereby synchronize an uplink signal, or enables the terminal to transmit an uplink signal at an uplink transmission point in time calculated by a satellite, in a mobile satellite communication system of an orthogonal frequency division multiple access (OFDMA) scheme or a single carrier frequency division multiple access (SC-FDMA) scheme.
2. Description of the Related Art
A mobile satellite communication system may use a Complementary Terrestrial Component (CTC) such as a repeater, a Complementary Ground Component (CGC), and an Ancillary Terrestrial Component (ATC). As a mobile satellite communication system, a Digital Multimedia Broadcasting (DMB) service is being provided in Korea, and researches regarding a Digital Video Broadcasting-Satellite services to Handhelds (DVB-SH) system are active in European countries in order to provide a broadcasting service from around 2010. Also, MSV and TerreStar of America are developing an integrated terrestrial satellite system for providing voice and data communications in urban areas and suburbs using the ATC.
The satellite DMB system of Korea is designed to additionally adopt a terrestrial network using, both a satellite and the same channel gapfiller to thereby enable a user to receive enhanced audio signals and multimedia signals using a receiver for a vehicle, a fixed terminal, or a mobile terminal. The satellite DMB system of Korea may be optimized in a band of 2630 MHz to 2655 MHz of the satellite and a terrestrial part. The satellite DMB system may include a feeder link earth station, a broadcasting satellite, two types of terrestrial repeaters, and a receiver, for example, a receiver for a vehicle, a fixed terminal, or a mobile terminal. Signals may be transmitted to the satellite via the feeder link earth station. In this instance, a Fixed Satellite Service (FSS) band, for example, 14 GHz may be used for an upward link. The received signals may be converted to the band of 2.6 GHz in the satellite, and be amplified to a desired level through an amplifier of a satellite repeater and thereby be broadcast to a service area. A system user may need to receive signals via a miniature antenna with a low directivity. For this, there is a need for a sufficient level of equivalent isotropically radiated power. Therefore, the satellite may need to include a large transmit antenna and a high power repeater. Major shortcomings found from a signal propagation in the band of 2.6 GHz may include an obstacle in a direct path from the satellite, and a shadowing. To overcome the shortcomings, a repeater to retransmit a satellite signal is added in a system design. This repeater is in charge of a portion occluded by an obstacle, for example, a building and the like. The repeater may be classified into a direct amplification repeater and a frequency converting repeater. The direct amplification repeater simply amplifies a broadcast signal of 2.6 GHz. Generally, a low gain amplifier may be used to avoid an unnecessary emission caused by signal interference between a receive antenna and a transmit antenna. The low gain amplifier is in charge of a relatively small region of up to 500 m based on a Line of Sight (LOS). The frequency converting repeater is in charge of a relatively large region of up to 3 km, and may convert the received signal of 2.6 GHz to a signal of a different frequency band, for example, 11 GHz and thereby transmit the converted signal. In this environment, a multi-path fading phenomenon where at least two signals are received may occur. In order to stably receive a multi-path fading signal, the satellite DMB system may use a rake receiver that is applied with a Code Division Multiplexing (CDM) technology.
The DVB-SH system of European countries may be a system that uses a satellite in the nationwide coverage and also uses a CGC in an indoor environment or a terrestrial coverage. The DVB-SH system aims to provide a mobile TV service in the bandwidth of 15 MHz of S band based on DVB-H. Since a band adjacent to a terrestrial International Mobile Telecommunication (IMT) band of the S band is used, an integration with a terrestrial IMT part may be readily performed. In addition, the terrestrial network may also be easily reused and thus costs may be reduced. The DVB-SH system considers a hybrid broadcasting structure with the terrestrial network. Also, in order to decrease signal interference between the satellite and the CGC, and to effectively use frequency resources, the DVB-SH system considers a structure where a reuse factor is set to “1” with respect to a CGC cell within a single satellite spot beam, and a reuse factor is set to “3” with respect to the satellite spot beam. In this case, in France, it is possible to broadcast, using the satellite spot beam, nine TV channels covering the entire nation, or to broadcast 27 channels via the terrestrial repeater in an urban area or in an indoor environment.
MSV and TerreStar of America are developing a geostationary orbit (GEO) based mobile satellite communication system in order to provide a personal communication service (PCS)/cellular terminal with a ubiquitous wireless wide area network service such as an Internet access, a voice communication, and the like in L band and S band. In America and Canada, by using a hybrid radio network structure where a satellite and an ATC are integrated, the GEO-mobile satellite communication system may provide a voice service or a high speed packet service via the ATC, that is, a terrestrial network in urban areas or populated areas, and may also provide a service via the satellite in suburbs or countryside not covered by the ATC. The ATC is in development to provide a satellite service without significantly increasing a complexity of a terrestrial terminal using a radio interface similar to a radio interface of the satellite, and the like.
A personal mobile satellite communication system to be developed aims to provide a service via a satellite in suburbs or countryside where a LOS is guaranteed, and to provide the service via an ATC in urban areas or indoor environments where a satellite signal is not guaranteed. Also, in order to decrease a chip set cost of a terminal, it may be important to design a radio interface of the satellite and a radio interface of the terrestrial terminal have some commonality. However, unique characteristics of the satellite, for example, a long propagation round trip delay time, a relatively large spot beam coverage, and the like may need to be minimized in order to reuse the radio interference of the terrestrial terminal for the satellite.